Mexican President Andres Manuel Lopez Obrador has met with the head of the largest U.S. labor group, the AFL-CIO.

Lopez Obrador’s office said Wednesday he promised AFL-CIO President Richard Trumka that Mexico will enforce new, stricter labor laws. He also called for ratification of the U.S.-Mexico-Canada free trade agreement.

President Trump took to Twitter on Labor Day to attack AFL-CIO President Richard Trumka, slamming him for his criticism of Trump’s trade deals. The AFL-CIO is the country’s largest coalition of more than 50 major unions and represents some 12.5 million American workers, from pilots to teachers.